Administration of 8 mg/gm monosodium glutamate to neonatal hamsters will cause a specific lesion limited to the arcuate nucleus of the hypothalamus. The time of administration of MSG has been found to be a critical factor in the reproductive neuroendocrine to MSG damage. We have found no alterations in the regulation of LH secretion but have found that FSH secretion is submaximal. We have also found that the injection of MSG does not have a direct effect on the ovary (as evidenced by enzyme activity, progesterone secretion & synthesis and the ability to be stimulated by endogenous gonadotropins). Work is in progress to determine the response to LH-RH stimulation of the anterior pituitary gland in MSG-treated animals.